Bearing arrangement

ABSTRACT

A bearing arrangement  2  comprising an outer race  10 , a shaft  4  arranged to rotate with respect to the outer race  10  thereby defining an axis of rotation  8  of the shaft  4 . The shaft  4  and the outer race  10  are arranged to define a region of overlap between the shaft  4  and the outer race  10  along the axis of rotation. An inner race  12  is disposed between the outer race  10  and the shaft  4  in the region of overlap and coupled for rotation with the shaft  4 , the inner race  12  and the shaft  4  defining an annular reservoir  40  between them for accommodating radial expansion of the shaft  4  or radial displacement of the shaft  4  with respect to the axis of rotation  8.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromBritish Patent Application Number 1121162.0 filed 9 Dec. 2011, theentire contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a bearing arrangement.

2. Description of the Related Art

Roller bearings are often used to support driveshafts in turbineengines. Typically, each roller bearing comprises an inner race arrangedto rotate with the driveshaft, and an outer race fixed to the main bodyof the engine. Roller elements are disposed between the inner and outerraces to allow rotation of the races with respect to each other.

In use, the driveshaft is exposed to elevated temperatures which heatthe driveshaft and cause it to expand radially. The temperaturedistribution along the shaft is often non-uniform which causes differentamounts of radial expansion along its length. For example, a driveshaftwhich is attached at one end to a turbine disc, and is supported by abearing cooled by oil has a temperature gradient which decreasesgradually from the end of the shaft attached to the turbine disc towardsthe end of the shaft supported by the bearing. The temperature variationcreates a corresponding decrease in the diameter of shaft from the hotend of the shaft towards the cold end. This phenomenon is known asconing.

Coning can be particularly problematic when it occurs in the vicinity ofthe bearings since it can lead to uneven loading across the bearing. Inparticular, it can increase edge loading of the bearing races. This isundesirable because it creates uneven stress distributions across thebearing which can reduce the operational life of the bearings.Furthermore, where bearings are preloaded, for instance to minimiseskidding of lightly loaded rolling elements, the problem is exacerbated.Coning can also occur in the inner and outer races of the bearing.

OBJECTS AND SUMMARY OF THE INVENTION

There is therefore a need for a bearing arrangement which alleviates theimpact of coning.

According to a first aspect of the invention there is provided a bearingarrangement comprising a stationary component, a rotary componentarranged to rotate with respect to the stationary component therebydefining an axis of rotation of the rotary component, the rotarycomponent and the stationary component being arranged to define a regionof overlap between the rotary component and the stationary componentalong the axis of rotation; and an intermediate component disposedbetween the stationary component and the rotary component in the regionof overlap and coupled for rotation with the rotary component, theintermediate component and the rotary component defining an annularreservoir between them for accommodating radial expansion of the rotarycomponent or radial displacement of the rotary component with respect tothe axis of rotation. The term “stationary” means does not rotate aboutthe axis of rotation when in use. The stationary component is thereforea component which may form part of a supporting structure such as abearing housing with respect to which the rotary component rotates.

The stationary component may define a bearing axis, wherein theintermediate component has an axis of rotation which is arranged toextend parallel with the bearing axis, and the annular reservoir isarranged to accommodate radial expansion or radial displacement of therotary component such that the axis of rotation of the intermediatecomponent remains parallel with the bearing axis during use.

The intermediate component and the rotary component may be supported forrotation by the stationary component.

The annular reservoir may be filled with a fluid. The fluid may providea film about the rotary component by which the rotary component issupported. The depth of the film may vary to accommodate the radialexpansion or the radial displacement of the rotary component. The amountof fluid in the reservoir may be varied to adjust the depth of the film.The fluid may be a liquid. The fluid may be a pressurised fluid.

The stationary component may be disposed radially outwardly of therotary component with respect to the axis of rotation.

The stationary component may be an outer race and the intermediatecomponent may be an inner race, wherein rolling elements are disposedbetween the outer race and the inner race.

The rotary component may be a shaft supported for rotation by the innerrace.

The stationary component may be disposed between a second stationarycomponent and the rotary component, wherein the stationary component iscoupled to the second stationary component to prevent rotation of thestationary component with respect to the second stationary component,the stationary component and the second stationary component defining asecond annular reservoir between them for accommodating radial expansionof the stationary component or radial displacement of the stationarycomponent with respect to the axis of rotation.

The second stationary component may be disposed radially outwardly ofthe stationary component with respect to the axis of rotation.

The second stationary component may be a hub structure for supportingthe stationary, intermediate and rotary components. The second annularreservoir may be filled with a fluid.

According to a second aspect of the invention there is provided aturbine comprising a bearing arrangement according to the first aspectof the invention wherein the rotary component is a driveshaft of theturbine.

According to a third aspect of the invention there is provided an enginecomprising a bearing arrangement in accordance with the first aspect ofthe invention, the engine having an engine axis, wherein the rotarycomponent is a driveshaft of the engine, the intermediate component hasan axis of rotation which is arranged to extend parallel with the engineaxis, and the annular reservoir is arranged to accommodate radialexpansion or radial displacement of the rotary component such that theaxis of rotation of the intermediate component remains parallel with theengine axis during use.

The stationary component may be a first race and the intermediatecomponent may be a second race, wherein rolling elements are disposedbetween the first race and the second race.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the accompanying drawings, in which:

FIG. 1 is sectional view of a bearing arrangement;

FIG. 2 is a sectional view of the bearing arrangement of FIG. 1 in use;and

FIG. 3 is a sectional view of a variant of a bearing arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a stub-shaft assembly 2 comprising a shaft 4, for example amain driveshaft of a gas turbine, supported by a roller bearing 6. Theshaft 4 defines a rotational axis 8 about which the shaft 4 rotates. Thebearing 6 comprises an outer race 10 and an inner race 12, between whichrollers 14 are disposed. The inner and outer races 10, 12 are annular.The inner and outer races 10, 12 may each have cylindrical cross-sectionor may be lobed, for example the outer race 10 shown in FIG. 1 may be atri-lobed ring. The rollers 14 are held for rotation by a cage 16 and bya groove 17 in the radially outer surface of the inner race 12 whichrestricts axial displacement of the rollers 14.

The shaft 4 is hollow and has a radially outer surface 18 and a radiallyinner surface 20. The shaft 4 comprises a recess 22 formed in the outersurface of the shaft 4 towards an end of the shaft 4. The recess 22extends circumferentially about the entire shaft 4. The recess 22 has abottom surface 24 which extends parallel to the rotational axis 8 andopposing side surfaces 26 that are perpendicular to the rotational axis8. In the embodiments shown, the recess 22 is formed by an end piece 28bolted onto a main portion 30 of the shaft 4. The width of the recess 22is defined in the direction of the rotational axis 8. Anti-rotation dogs32 are disposed at the end of the shaft 4 and adjacent the recess 22.The anti-rotation dogs 32 extend radially outwardly from the shaft 4.

The inner race 12 has a radially outer surface 34 and a radially innersurface 36. The width of the inner race 12 corresponds to the width ofrecess 22. The inner race 12 is disposed in the recess 22 such that theradially inner surface 36 of the inner race 12 is parallel with thebottom surface 24 of the recess 22. The inner race 12 defines end gaps37 between the sides of the inner race 12 and the side surfaces 26 ofthe recess 22. The end gaps 37 provide leakage paths for oil. The endgaps 37 may be formed to tight tolerances in order to provide apredetermined amount of leakage flow during use. Passages 39 are alsoprovided through the inner race 12 for the supply of oil to the rollers14.

The inner race 12 has slots 38 in one side of the race 12 for receivingthe anti-rotation dogs 32 in order to couple the inner race 12 forrotation with the shaft 4. The slots 38 allow the anti-rotation dogs 32to move radially with respect to the rotational axis 8. The shaft 4 isthus able to move in a radial direction with respect to the inner race12.

The radially inner surface 36 of the inner race 12 and the bottomsurface 24 and side surfaces 26 of the recess 22 define an annularreservoir 40 between the inner race 12 and the shaft 4. A conduit 42extends through the wall of the shaft 4, from the inner surface 20 ofthe shaft 4 to the bottom surface 24 of the recess 22. The conduit 42provides communication between the interior of the shaft 4 and thereservoir 40. Two circumferential recesses 45 are provided in the bottomsurface 24 of the recess 22. The circumferential recesses 45 aredisposed on opposing sides of the conduit 42 with respect to the axialdirection of the shaft 4. Respective sealing rings 43, such as pistonrings, are disposed within the circumferential recesses 45 and sealagainst the radially inner surface 36 of the inner race 12.

The outer race 10 is supported by a housing 44 (shown in part only). Thehousing 44 and the outer race 10 define an oil chamber 46 about the endof the shaft 4 and the inner race 12, roller elements 14 and cage 16.

In use, oil is supplied under pressure to the oil chamber 46 so that theend of the shaft 4, including the radially inner and outer surfaces 18,20, inner race 12, rollers 14 and cage 16 within the chamber 46 arewashed in oil, but not completely immersed. Oil flows through theconduit 42 to flood the reservoir 40. The sealing rings 43 restrict flowfrom the reservoir 40 through the end gaps 37. The shaft 4 is thereforesupported by a film of oil between the bottom surface 24 of the recess22 and the radially inner surface 36 of the inner race 12. The loadtransmitted by the shaft 4 on the inner race 12 is evenly distributed bythe oil.

As the temperature of the shaft 4 increases, it expands radially. Theradial expansion can be accommodated by displacement of the oil withinthe reservoir 40. The radial expansion causes a reduction in the volumeof the reservoir 40 and this can be accommodated by expulsion of oilfrom the reservoir 40 past the sealing rings 43 and through the end gaps37 into the oil chamber 46. The sealing rings 43 may be arranged toallow expulsion of oil only when the pressure within the reservoir 40 isnot less than a predetermined pressure. The predetermined pressure may,for example, correspond to a particular reservoir geometry or loadingcondition of the shaft 4, Expansion of the shaft 4 thus reduces thedepth of the film of oil supporting the shaft 4 in the region of theexpansion.

Where a temperature variation along the portion of shaft 4 supported bythe oil causes a variation in the amount of radial expansion along theshaft 4, the difference in expansion can be accommodated byredistribution or expulsion of the oil from the reservoir 40. The shaft4 remains supported by the redistributed or remaining oil so that theload transmitted by the shaft 4 through the inner race 12 remains evenlydistributed.

It will be appreciated that rotation of the shaft 4 causes rotation ofthe inner race 12 and hence rotation of the reservoir 40. Skin frictionbetween the oil and the inner race 12 and the shaft 4 will thereforecause the oil to rotate within the reservoir 40. This can generate acentrifugal effect within the reservoir 40 thereby increasing thepressure of the oil in the region of the reservoir 40 adjacent the innerrace 12.

The reservoir 40 may also accommodate displacement of the shaft 4 withrespect to the inner race 12. The oil in the reservoir 40 may thereforeact to damp oscillations of the shaft 4, for example, oscillationscaused by vibration of the shaft 4.

Oil may be fed by under track jetting or through a pressurised system.The reservoir 40 may be connected to the main oil chamber 46, asdescribed above. Alternatively, the reservoir 40 may be connected to anindependent oil feed system which may comprise an independent pressureregulator.

The outer race 10 abuts a radially outward surface of the housing 44(not shown) and thus provides circumferential support of the outer race10 and prevents deformation of the outer race 10 when loaded.

FIG. 2 shows a variant of the stub-shaft assembly shown in FIG. 1, inwhich the oil is jetted under pressure from a nozzle 47 in the casing 44in the general direction of the conduit 42.

FIG. 3 shows a similar stub-shaft assembly 2 and bearing 6 arrangementin which a second reservoir 48 is provided between the outer race 10 andthe housing 44. The outer race 10 is coupled to the housing 44 byanti-rotation dogs 50 provided on the casing 44 which engage with slots52 provided on the outer race 10 to prevent rotation of the outer racewith respect to the housing 44. The second reservoir 48 is static withrespect to the housing 44 during use.

The second reservoir 48 is supplied with oil via a second conduit 54through the housing 44. The oil in the second reservoir 48 supports theouter race 10. The bearing 6 is therefore supported by a second film ofoil between the bearing 6 and the housing 44. The second film of oilaccommodates coning of the components of the stub-shaft assembly 2 andthe bearing 6, in particular coning of the outer race 10 of the bearing6. Consequently, in use, the rollers 14 and the inner and outer races10, 12 remain parallel with the rotational axis 8 when coning occurs. Inaddition, the second film of oil allows for radial displacement of thestub-shaft assembly 2 and the bearing with respect to the rotationalaxis 8. The shaft 4 therefore remains located when the stub-shaftassembly 2 runs out of balance or coning occurs. Consequently, edgeloading on the bearing races 10, 12 is reduced, or avoided entirely.

It will be appreciated that the arrangement of the slots 38, 52 and theanti-rotation dogs 32, 50 could be reversed so that the anti-rotationdogs are provided on the inner and outer races 12 and the correspondingslots are provided on the shaft 4 and housing 44 respectively. It willbe further appreciated that other means suitable for rotatably securingthe inner race 12 with the shaft 4 or the outer race 10 with the housing44 may be used.

We claim:
 1. A bearing arrangement comprising: a stationary component; arotary component arranged to rotate with respect to the stationarycomponent thereby defining an axis of rotation of the rotary component,the rotary component and the stationary component being arranged todefine a region of overlap between the rotary component and thestationary component along the axis of rotation; and an intermediatecomponent disposed between the stationary component and the rotarycomponent in the region of overlap and coupled for rotation with therotary component, the intermediate component and the rotary componentdefining an annular reservoir between them for accommodating radialexpansion of the rotary component or radial displacement of the rotarycomponent with respect to the axis of rotation.
 2. A bearing arrangementas claimed in claim 1, wherein the stationary component defines abearing axis, the intermediate component having an axis of rotationwhich is arranged to extend parallel with the bearing axis, and theannular reservoir being arranged to accommodate radial expansion orradial displacement of the rotary component such that the axis ofrotation of the intermediate component remains parallel with the bearingaxis during use.
 3. A bearing arrangement as claimed in claim 1, whereinthe intermediate component and the rotary component are supported forrotation by the stationary component.
 4. A bearing arrangement asclaimed in claim 1, wherein the annular reservoir is filled with afluid.
 5. A bearing arrangement as claimed in claim 4, wherein the fluidprovides a film about the rotary component by which the rotary componentis supported.
 6. A bearing arrangement as claimed in claim 5, whereinthe depth of the film varies to accommodate the radial expansion or theradial displacement of the rotary component.
 7. A bearing arrangement asclaimed in claim 6, wherein the amount of fluid in the reservoir isvaried to adjust the depth of the film.
 8. A bearing arrangement asclaimed in claim 4, wherein the fluid is a liquid.
 9. A bearingarrangement as claimed in claim 4, wherein the fluid is a pressurisedfluid.
 10. A bearing arrangement as claimed in claim 1, wherein thestationary component is disposed radially outwardly of the rotarycomponent with respect to the axis of rotation.
 11. A bearingarrangement as claimed in claim 10, wherein the stationary component isan outer race and the intermediate component is an inner race, whereinrolling elements are disposed between the outer race and the inner race.12. A bearing arrangement as claimed in claim 11, wherein the rotarycomponent is a shaft supported for rotation by the inner race.
 13. Abearing arrangement as claimed in claim 1, wherein the stationarycomponent is disposed between a second stationary component and therotary component, the stationary component being coupled to the secondstationary component to prevent rotation of the stationary componentwith respect to the second stationary component, the stationarycomponent and the second stationary component defining a second annularreservoir between them for accommodating radial expansion of thestationary component or radial displacement of the stationary componentwith respect to the axis of rotation.
 14. A bearing arrangement asclaimed in claim 13, wherein the second stationary component is disposedradially outwardly of the stationary component with respect to the axisof rotation.
 15. A bearing arrangement as claimed in claim 13, whereinthe second stationary component is a hub structure for supporting thestationary, intermediate and rotary components.
 16. A bearingarrangement as claimed in claim 13, wherein the second annular reservoiris filled with a fluid.
 17. A turbine comprising a bearing arrangementas claimed in claim 1, wherein the rotary component is a driveshaft ofthe turbine.
 18. An engine comprising a bearing arrangement as claimedin claim 1, the engine having an engine axis, wherein the rotarycomponent is a driveshaft of the engine, the intermediate component hasan axis of rotation which is arranged to extend parallel with the engineaxis, and the annular reservoir is arranged to accommodate radialexpansion or radial displacement of the rotary component such that theaxis of rotation of the intermediate component remains parallel with theengine axis during use.
 19. An engine as claimed in claim 18, whereinthe stationary component is a first race and the intermediate componentis a second race, and rolling elements are disposed between the firstrace and the second race.